Drawings and design from live projects

The brief was a covered loading bay against an existing building: 14 m wide, 23 m long, with five frames at 5.75 m centres. One long elevation had to stay completely open so lorries could reverse in between the columns. That single requirement changes the design from a routine shed into a stability problem.

The frames use 457×191 UB 74 columns, about 7 m tall, and 356×171 UB 57 rafters at a 7° pitch, all in S355 steel. The rafters are deepened at the corners and the ridge with haunches cut from the same section, joined with 20 mm end plates, M20 grade 8.8 bolts and 10 mm stiffeners to stop the flanges buckling under the corner moment.

Because the open face cannot be braced, all longitudinal stability comes from the closed sides: cross bracing in 88.9 mm CHS tubes in two bays of the back wall and across the gable, and 114.3 mm CHS bracing in the roof plane of the end bays, tied together by 203×133 UB 25 eaves beams. The column bases are 650×250×15 mm plates on four M20 anchor rods, designed as nominally pinned.

The open side was treated as a dominant opening for wind to EN 1991-1-4, using an internal pressure coefficient of 0.9 because the opening is more than three times the area of all other openings combined. The frame was checked for second-order sway effects, and the open-side columns were designed for lateral torsional buckling over their full unrestrained 7 m height.

The column size was larger than first expected, so the design was benchmarked against typical UK portal frames of this span. The rafters sit in the normal range. The columns are heavier than an enclosed shed would need, and every reason for that is a real load effect of the open side, not a margin added by feel. The design also requires impact protection so reversing lorries cannot strike the columns.

A garage is built to keep the rain off a car, not to be a home. A trial pit beside the side wall showed how this one was built: single-skin brickwork on strip footings, with the top of the concrete 675 mm below ground, stepping out 200 mm from the masonry, about 800 mm deep overall and 450 to 500 mm wide.

Inside, a new partition in 7.3 N blockwork is tied to the existing elevation with wall starters. It sits on 500 mm wide trenchfill in GEN 3 concrete, taken down to the same depth as the existing footings.

Above, a timber buttress partition of 38×89 CLS studs at 400 mm centres is overboarded with 9.5 mm OSB, glued and nailed at 150 mm centres. It is strapped and cross-lapped to the head of the external wall, with straps running 1.5 m down the inside face of the brickwork at 1 m centres.

The new structure is carried on steelwork: a 203×102 UB 23 with a 6 mm bottom plate fixed by 4 mm hit-and-miss fillet welds and 300 mm end bearings, plus 152×152 UC 23 and 152×89 UB 16 members. They are joined with 10 mm end plates and four M16 grade 8.8 bolts. At the corner, a 200×100×10 unequal angle welded to the column end gives it a seat on the brickwork.

Modern roofs are usually built from factory-made trussed rafters. Each truss is a triangle in which every member relies on the others, and the bottom ties are sized to carry a plasterboard ceiling, not people and furniture.

So the new floor is carried independently. 203×102 UB 23 steel beams in grade S275 run gable to gable, and 47×175 C24 joists at 400 mm centres hang between them in face-fixed joist hangers on timber packers, bolted to the steel webs with M10 grade 8.8 bolts.

Where trusses are cut for the dormer and the stairwell, trebled 47×195 C24 trimmers pick up the cut members and bear 100 mm onto the inner block leaf. A 152×89 UB 16, profiled to the roof pitch, carries the dormer front, with a steel packer plate and a 200 mm packer so the timber above is not crushed. The dormer cheeks are 38×140 CLS studs at 400 mm centres, sheathed in OSB and fixed to the blockwork with M10 resin anchors.

Each existing truss at 600 mm centres is supplemented with a 47×150 C24 rafter, and extra rafters are added between them so spacing never exceeds 300 mm. Steel-to-steel joints use 10 mm knife plates and 660 mm long 200×100×10 angle spreaders with M12 grade 8.8 bolts.

The garage forms the side structure to an existing single-storey property, and the client wanted to convert it to habitable space. Three boreholes and trial pits were sunk to prove the ground and expose the neighbour’s existing footings. They found coarse sands and gravels, likely river terrace deposits, on which traditional foundations could safely be formed.

Because the new foundations sat directly against the boundary, a standard strip footing risked undermining the neighbouring wall. A stepped cantilever foundation was designed instead, using a deeper concrete section as a counterweight to keep the structure stable. The superstructure design covered the new flat roof, the masonry leaf and a steel beam over the opening, all checked to Eurocode, including wind pressure zones to EN 1991-1-4.

Trial pits revealed a blue-grey cohesive clay with peat inclusions and a perched water table entering at around 1.5 m. The clay has a medium volume-change potential, and the plot is ringed by willow, hawthorn and leylandii, all drivers of seasonal ground movement.

Founding depths were set using the NHBC tree and clay tables: up to 2.4 m where leylandii sit close to the works. The workshop was given pad foundations at depth in FND2 sulphate-resisting concrete. The residential extensions were steered away from ground-bearing slabs toward suspended floors, to allow for long-term heave as the ground recovers from removed trees.

Bi-fold doors are unforgiving of movement, so the supporting steel was sized for a deflection limit of under 1 mm rather than strength alone. A 178 UB with a welded bottom plate was detailed, with the connection arranged to bear cleanly onto the masonry and the timber lantern trimmers framing in above.

The design also has to deal with torsion, a twist along the length of the beam. It happens because the facing brickwork and the door itself sit outside the centre of the steel beam, cantilevered off the bottom plate. Torsion can only develop if the ends of the beam are restrained against twist, so the bottom plate extends onto the facing brickwork at each end of the opening, welded to the beam, and is designed to take the full torsion at each end as a buckling moment.

The welds are designed to resist the cantilevered loads, and also to limit heat-induced buckling of the steel as the weld is laid. That is done by specifying a hit-and-miss weld, allowing for deflection of the bottom plate between each length of weld.

The package included the timber trimmer design for the roof lantern and the bolt, plate and weld specification for the steel, every member checked to the relevant Eurocode and issued as buildable details.

One of the most common questions we’re asked is a simple one: “is this wall load-bearing, or can I just knock it through?” Before any internal wall is removed to open up a kitchen-diner or through-lounge, it needs checking. A wall that carries a floor, roof or another wall above cannot simply be taken down without a beam in its place.

We carry out a site survey to establish whether the wall is load-bearing (structural) or a non-load-bearing partition, such as a stud wall. That means looking at what sits above it: which way the floor joists run, whether a wall or roof loads onto it, and how the property is built, rather than guessing from the wall’s thickness.

The survey gives you a clear answer. Where the wall is structural, it tells you exactly what is needed to remove it safely: typically a steel beam (an RSJ) with properly designed padstones at each end. Where the wall turns out to be non-structural, we can confirm it is safe to take down without a beam, saving you unnecessary cost.

You receive a written assessment for your builder and, where a beam is needed, structural calculations and a beam specification for Building Control: everything needed to knock through with confidence.

Class Q permitted development turns on a single structural test: is the existing building genuinely capable of conversion, or would the scheme depend on new primary structure to stand up? Planning Practice Guidance and recent appeal decisions are clear that Class Q is a conversion right, not a rebuild right, and a submission lives or dies on whether the structural evidence supports that distinction.

The survey opens with a full visual inspection of the frame (principal posts, tie beams, purlins and rafters), recording species, section sizes, connection type and condition, alongside the walling that encloses each bay. Decay, insect attack, historic alteration, out-of-plumb movement and earlier repairs are logged bay by bay and cross-referenced to an annotated plan and elevation, so every finding traces back to a specific structural element.

That record is then set against the proposed layout: which frame members, floors and roof coverings are kept as they are, which are repaired like for like, and confirmation that no new load-bearing elements, foundations or structural floors are needed to make the building stand up. Where an element is beyond economic repair, the report distinguishes a genuine like-for-like replacement from a change that would tip the scheme into rebuild territory.

The output is a structural appraisal report, submitted with the architect’s drawings and the planning consultant’s statement of case, giving the local planning authority an evidenced basis for confirming the building can be converted without new structure.